Power converters/adapters are typically used to charge and/or power portable electronic devices. These converters may provide a programmable voltage and/or current to the target device.
Prior art converters/adapters architectures fail to provide for compensating voltage drops in the output cable extending between the converter/adapter and the target device. This meant that output cables had to be sized with large AWG wire to minimize the IR drops and that open circuit (no load) output voltage had to be programmed high to minimize the effects of the drops. Also, output cables had to be limited to a maximum length for a given wire gauge so the drops at high curl did not become excessive.
Some prior art tips coupled between the cable and target device accommodate for cable drops, but this solution uses 2 more wires in the cable and tip to achieve the correction, as shown in FIG. 1. A single wire solution would have only compensated for half the drop passively and would have required an active stage to compensate for the entire drop on the positive and negative leads. The active compensation would have placed a length restriction on output cable as well.
The Voltage programming used a resistor in the tip that was connected in parallel with a voltage sampling potentiometer chain in the converter/adapter (base unit). This tip resistor shared a common ground with the high current ground return, so any load transients in the cable ground lead were transmitted back to the base unit and undesirably affected the output voltage.
The voltage programming was limited to a pre-set minimum voltage defined by the reference in the base unit. This meant that no passive tip could force the base unit output voltage below the preset minimum (thus, no ability to upgrade the power supply to operate over a wider voltage range other than changing the base unit).
The voltage programming resistor in the tip was included in the overall feedback loop along with the cabling from the base unit to the programming resistor. This puts a portion of the feedback loop outside the base unit, making loop compensation more difficult.
In this example of FIG. 1, note the IL load current flows through the ground path shared by resister Rvset. Noise or transients on this ground, or picked up by the Vsense line, cannot be filtered by the addition of bypass capacitors (across resistor R2 or resistor Rvset) as this would place an extra low frequency pole on integrator U1 outside its local feedback loop. This external low frequency pole would make the feedback loop compensation difficult and degrade the transient response of the base unit. Also, the distributed capacitance of the cable itself produces a similar pole at higher frequencies, again contributing to problems in compensating the feed back loop.